For metered supply of a powdery substance or a granular substance, a belt conveyor, for example, has been used. The metered supply of a powdery substance or a granular substance by the use of a belt conveyor is accomplished by installing a switching gate or a roller over the conveyor thereby setting the thickness of the layer of the powdery or granular substance being forwarded on the conveyor at a prescribed value. When the conventional belt conveyor of the type described above is used for the purpose of transferring a viscous wet material such as a hydrated gel of hydrophilic polymer, such as absorbent resin, it is difficult to attain metered conveyance or supply of the wet material.
The gate or roller disposed above the belt conveyor is actuated while the hydrated gel of absorbent resin delivered to the incoming end of the belt conveyor is in the process of transfer in the direction of the outgoing end the thickness of the layer of the hydrated gel of absorbent resin on the conveyor is regulated to a fixed value. Since the hydrated gel possesses viscosity, it is destined to gain in bulk density when it is compacted under the pressure exerted thereon in the region of the gate. Once this increase of bulk density occurs, the metered supply of the hydrated gel can no longer be obtained with high accuracy because the hydrated gel being transferred in the form of a layer of a fixed thickness from the outgoing end of the belt conveyor to the next step of drying has undergone changes in specific gravity and volumetric ratio from the initial state. Further, since the increased bulk density results in degrading the permeability of the hydrated gel to the air, the hot air is incapable of permeating into the interior of the layer of hydrated gel and fulfilling a continuous drying work throughout the entire volume of the layer of hydrated gel and consequently part of the layer of hydrated gel remains undried.
Particularly for the purpose of drying a viscous material such as, for example, a wetted material, an aerating band type drier incorporating therein a band conveyor may be used. When this drier is used for drying the aforementioned hydrated gel, which has been compacted by pressure and consequently degraded in permeability to the air, the hot air is not sufficiently passed through the layer of the hydrated gel and the interior of the layer of the hydrated gel is dried very poorly. Thus, the layer of the hydrated gel reaching the outlet part of the drier inevitably contains an undried part. In the next step of pulverization, the undried part of the hydrated gel escapes pulverization and consequently adheres to and clogs the apparatus even to the extent of not only interfering with the work of continuous drying but also causing breakage of the apparatus in an extreme case.
Particularly when the hydrated gel of hydrophilic polymers such as absorbent resin is obtained by polymerizing a monomer component containing 50 to 100% by weight of acrylic acid (or a salt thereof), the disadvantage described above becomes all the more conspicuous because the viscosity exhibited independently or mutually by the individual particles of the gel is very high.
This invention has been produced by the urge to fulfill the imperfect prior art described above. When a material delivered to the incoming end of a conveyor is advanced in a large heap on the conveyor, given a fixed thickness by the use of a gate and then transferred in a prescribed rate to the next step, it must be released in a loose state to the next step even if the material is a wet substance. When the wet material in the process of transfer toward the outgoing end of the conveyor is given a small thickness by the gate, the wet material slips on the upper surface of the conveyor and cannot be effectively transferred by the conveyor.
When the wet material is given a sufficiently large thickness by the gate so as to avoid the phenomenon of slippage, it is not released in a loose state from the outgoing end of the conveyor. When the layer of the wet material is set at the aforementioned sufficiently large thickness by means of the gate, the bulk density of the wet material is increased throughout the entire width extent of the thickness. By causing the upper side part of the layer of the wet material to be scraped off with a scraping member and, meanwhile, allowing the lower side part thereof not discharged by the scraping member to be released from the outgoing end of the conveyor, the wet material can be continuously conveyed to the next step without being wholly compacted by pressure.
An object of this invention, therefore, is to provide a method for metering the supply of a material which permits therefor material to be transferred in a prescribed rate with high accuracy to the next step and an apparatus to be used therefor.
Another object of this invention is to provide a method for the efficient production of a hydrophilic polymer by causing a hydrated gel of hydrophilic polymer obtained by batch polymerization to be delivered in a prescribed rate with high accuracy into a drier and dried therein with high efficiency.